Likely Developing La Niña Captured in New 3-D Animation of Pacific Water Temperatures

Chris Dolce
Published: May 17,2016
A new 3-D animation is giving us a glimpse of what is likely a developing La Niña event in the equatorial Pacific Ocean.
The animation created by NOAA is a cross section of water temperatures analyzed near the equator, from the ocean's surface to about 1,000 feet deep. Blue shadings represent colder than average water temperatures while red shaded areas are warmer than average.
Surface water temperatures in the equatorial Pacific Ocean are above average during El Niño events and below average when La Niña is present. In general, how far above/below the water temperatures are in the so-called Nino 3.4 region - a part of the central equatorial Pacific Ocean - dictates the strength of a given El Niño or La Niña episode.
In the first part of the animation with the date March 14,2016, you can see a large area of surface water that was still above average from the central Pacific Ocean eastward to near South America. As the graphic evolves through April and into early May, the once widespread pool of warm water contracts to just a small part of the central Pacific, signaling the continued demise of El Niño in spring.

Animation shows the fading warmer than average water in the equatorial Pacific Ocean being replaced with cooler than average water.

Given the building area of cooler waters as shown in the animation, NOAA raised the likelihood of La Niña's development to a 75 percent chance in their May outlook.
(MORE: 75 Percent Chance of La Niña Development)
In fact, the large majority of model forecasts suggest the equatorial waters may become cooler than average this summer, potentially even swinging into La Niña as early as this fall. A few ensemble forecasts even have a strong La Niña forecasted by late summer or fall.
We can also see the changing water temperatures in the equatorial Pacific Ocean by just just looking at water temperatures on the surface of the ocean.
Notice in this animation the fading orange shadings from March into early May. By the last part of the animation you can even see a few splotches of blue depicting cooler than average water temperatures in the eastern equatorial Pacific Ocean.

Sea-surface temperatures from March 2016 into early May 2016.

What Does the Development of La Niña Mean For Winter 2016-17?

The strength of any potential developing La Niña will dictate the impacts we'll see worldwide later this fall and into next winter.
We've said many times an El Niño, La Niña, or the lack of either, known as the neutral phase, is only one large-scale forcing on the atmosphere. It is not the be-all and end-all determining whether a season is wet, dry, cold or warm.
Despite that, the peak atmospheric response to the equatorial Pacific anomalies tends to occur in the northern hemisphere winter months.
So, in the event we have a La Niña settling in by fall or winter, let's take a look at December-February U.S. temperature and precipitation anomalies during weak (SST anomalies from 0.5 to 0.9 degrees below average), moderate (1.0 to 1.4 degrees below average) and strong (1.5 degrees below average or cooler) La Niñas.
Temperatures
While there are some differences among La Niña magnitudes, some commonalities emerge regarding La Niña winter forcing in the U.S.:

• Cold: Northern Plains, Upper Midwest, New England, New York state, West Coast
• Warm: Southern Plains, Southeast

Neglecting other factors, it appears the stronger the La Niña, the stronger the likelihood the winter warmth spreads farther north into the Corn Belt, Ohio Valley and Mid-Atlantic states.

December-February temperature anomalies (degrees Fahrenheit) during 11 weak, 6 moderate, and 3 strong La Niña events dating to 1950, using the classification scheme from Jan Null.

Precipitation
Again, despite some differences among La Niña magnitudes, some commonalities are apparent:

• Wet: Pacific Northwest, Bitterroots (western Montana/Idaho), parts of the Ohio Valley, Tennessee Valley
• Dry: Southern Plains, Gulf/Southeast coast including Florida, Southern California, Desert Southwest

December-February precipitation anomalies (inches) during 11 weak, 6 moderate, and 3 strong La Niña events dating to 1950, using the classification scheme from Jan Null.